
/***************************************************************************
                                                                           *
Copyright 2013 CertiVox UK Ltd.                                           *
                                                                           *
This file is part of CertiVox MIRACL Crypto SDK.                           *
                                                                           *
The CertiVox MIRACL Crypto SDK provides developers with an                 *
extensive and efficient set of cryptographic functions.                    *
For further information about its features and functionalities please      *
refer to http://www.certivox.com                                           *
                                                                           *
* The CertiVox MIRACL Crypto SDK is free software: you can                 *
  redistribute it and/or modify it under the terms of the                  *
  GNU Affero General Public License as published by the                    *
  Free Software Foundation, either version 3 of the License,               *
  or (at your option) any later version.                                   *
                                                                           *
* The CertiVox MIRACL Crypto SDK is distributed in the hope                *
  that it will be useful, but WITHOUT ANY WARRANTY; without even the       *
  implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. *
  See the GNU Affero General Public License for more details.              *
                                                                           *
* You should have received a copy of the GNU Affero General Public         *
  License along with CertiVox MIRACL Crypto SDK.                           *
  If not, see <http://www.gnu.org/licenses/>.                              *
                                                                           *
You can be released from the requirements of the license by purchasing     *
a commercial license. Buying such a license is mandatory as soon as you    *
develop commercial activities involving the CertiVox MIRACL Crypto SDK     *
without disclosing the source code of your own applications, or shipping   *
the CertiVox MIRACL Crypto SDK with a closed source product.               *
                                                                           *
***************************************************************************/
/*
 *   MIRACL arithmetic routines 0 - Add and subtract routines
 *   mrarth0.c
 *
 */
#include "miracl.h"

void mr_padd(_MIPD_ big x, big y, big z)
{ /*  add two  big numbers, z=x+y where *
   *  x and y are positive              */
    int       i, lx, ly, lz, la;
    mr_small  carry, psum;
    mr_small *gx, *gy, *gz;
#ifdef MR_OS_THREADS
    miracl* mr_mip = get_mip();
#endif
    lx = (int)x->len;
    ly = (int)y->len;

    if (ly > lx) {
        lz = ly;
        la = lx;
        if (x != z)
            copy(y, z);
        else
            la = ly;
    } else {
        lz = lx;
        la = ly;
        if (y != z)
            copy(x, z);
        else
            la = lx;
    }
    carry  = 0;
    z->len = lz;
    gx     = x->w;
    gy     = y->w;
    gz     = z->w;
    if (lz < mr_mip->nib || !mr_mip->check) z->len++;
#ifndef MR_SIMPLE_BASE
    if (mr_mip->base == 0) {
#endif
        for (i = 0; i < la;
             i++) { /* add by columns to length of the smaller number */
            psum = gx[i] + gy[i] + carry;
            if (psum > gx[i])
                carry = 0;
            else if (psum < gx[i])
                carry = 1;
            gz[i] = psum;
        }
        for (; i < lz && carry > 0;
             i++) { /* add by columns to the length of larger number (if there
                       is a carry) */
            psum = gx[i] + gy[i] + carry;
            if (psum > gx[i])
                carry = 0;
            else if (psum < gx[i])
                carry = 1;
            gz[i] = psum;
        }
        if (carry) { /* carry left over - possible overflow */
            if (mr_mip->check && i >= mr_mip->nib) {
                mr_berror(_MIPP_ MR_ERR_OVERFLOW);
                return;
            }
            gz[i] = carry;
        }
#ifndef MR_SIMPLE_BASE
    } else {
        for (i = 0; i < la; i++) { /* add by columns */
            psum  = gx[i] + gy[i] + carry;
            carry = 0;
            if (psum >= mr_mip->base) { /* set carry */
                carry = 1;
                psum -= mr_mip->base;
            }
            gz[i] = psum;
        }
        for (; i < lz && carry > 0; i++) {
            psum  = gx[i] + gy[i] + carry;
            carry = 0;
            if (psum >= mr_mip->base) { /* set carry */
                carry = 1;
                psum -= mr_mip->base;
            }
            gz[i] = psum;
        }
        if (carry) { /* carry left over - possible overflow */
            if (mr_mip->check && i >= mr_mip->nib) {
                mr_berror(_MIPP_ MR_ERR_OVERFLOW);
                return;
            }
            gz[i] = carry;
        }
    }
#endif
    if (gz[z->len - 1] == 0) z->len--;
}

void mr_psub(_MIPD_ big x, big y, big z)
{ /*  subtract two big numbers z=x-y      *
   *  where x and y are positive and x>y  */
    int       i, lx, ly;
    mr_small  borrow, pdiff;
    mr_small *gx, *gy, *gz;
#ifdef MR_OS_THREADS
    miracl* mr_mip = get_mip();
#endif
    lx = (int)x->len;
    ly = (int)y->len;
    if (ly > lx) {
        mr_berror(_MIPP_ MR_ERR_NEG_RESULT);
        return;
    }
    if (y != z)
        copy(x, z);
    else
        ly = lx;
    z->len = lx;
    gx     = x->w;
    gy     = y->w;
    gz     = z->w;
    borrow = 0;
#ifndef MR_SIMPLE_BASE
    if (mr_mip->base == 0) {
#endif
        for (i = 0; i < ly || borrow > 0; i++) { /* subtract by columns */
            if (i > lx) {
                mr_berror(_MIPP_ MR_ERR_NEG_RESULT);
                return;
            }
            pdiff = gx[i] - gy[i] - borrow;
            if (pdiff < gx[i])
                borrow = 0;
            else if (pdiff > gx[i])
                borrow = 1;
            gz[i] = pdiff;
        }
#ifndef MR_SIMPLE_BASE
    } else
        for (i = 0; i < ly || borrow > 0; i++) { /* subtract by columns */
            if (i > lx) {
                mr_berror(_MIPP_ MR_ERR_NEG_RESULT);
                return;
            }
            pdiff  = gy[i] + borrow;
            borrow = 0;
            if (gx[i] >= pdiff)
                pdiff = gx[i] - pdiff;
            else { /* set borrow */
                pdiff  = mr_mip->base + gx[i] - pdiff;
                borrow = 1;
            }
            gz[i] = pdiff;
        }
#endif
    mr_lzero(z);
}

static void mr_select(_MIPD_ big x, int d, big y, big z)
{ /* perform required add or subtract operation */
    int sx, sy, sz, jf, xgty;
#ifdef MR_FLASH
    if (mr_notint(x) || mr_notint(y)) {
        mr_berror(_MIPP_ MR_ERR_INT_OP);
        return;
    }
#endif
    sx = exsign(x);
    sy = exsign(y);
    sz = 0;
    x->len &= MR_OBITS; /* force operands to be positive */
    y->len &= MR_OBITS;
    xgty = mr_compare(x, y);
    jf   = (1 + sx) + (1 + d * sy) / 2;
    switch (jf) { /* branch according to signs of operands */
        case 0:
            if (xgty >= 0)
                mr_padd(_MIPP_ x, y, z);
            else
                mr_padd(_MIPP_ y, x, z);
            sz = MINUS;
            break;
        case 1:
            if (xgty <= 0) {
                mr_psub(_MIPP_ y, x, z);
                sz = PLUS;
            } else {
                mr_psub(_MIPP_ x, y, z);
                sz = MINUS;
            }
            break;
        case 2:
            if (xgty >= 0) {
                mr_psub(_MIPP_ x, y, z);
                sz = PLUS;
            } else {
                mr_psub(_MIPP_ y, x, z);
                sz = MINUS;
            }
            break;
        case 3:
            if (xgty >= 0)
                mr_padd(_MIPP_ x, y, z);
            else
                mr_padd(_MIPP_ y, x, z);
            sz = PLUS;
            break;
    }
    if (sz < 0) z->len ^= MR_MSBIT;           /* set sign of result         */
    if (x != z && sx < 0) x->len ^= MR_MSBIT; /* restore signs to operands  */
    if (y != z && y != x && sy < 0) y->len ^= MR_MSBIT;
}

void add(_MIPD_ big x, big y, big z)
{ /* add two signed big numbers together z=x+y */
#ifdef MR_OS_THREADS
    miracl* mr_mip = get_mip();
#endif
    if (mr_mip->ERNUM) return;

    MR_IN(27)

    mr_select(_MIPP_ x, PLUS, y, z);

    MR_OUT
}

void subtract(_MIPD_ big x, big y, big z)
{ /* subtract two big signed numbers z=x-y */
#ifdef MR_OS_THREADS
    miracl* mr_mip = get_mip();
#endif
    if (mr_mip->ERNUM) return;

    MR_IN(28)

    mr_select(_MIPP_ x, MINUS, y, z);

    MR_OUT
}

void incr(_MIPD_ big x, int n, big z)
{ /* add int to big number: z=x+n */
#ifdef MR_OS_THREADS
    miracl* mr_mip = get_mip();
#endif
    if (mr_mip->ERNUM) return;

    MR_IN(7)

    convert(_MIPP_ n, mr_mip->w0);
    mr_select(_MIPP_ x, PLUS, mr_mip->w0, z);

    MR_OUT
}

void decr(_MIPD_ big x, int n, big z)
{ /* subtract int from big number: z=x-n */
#ifdef MR_OS_THREADS
    miracl* mr_mip = get_mip();
#endif
    if (mr_mip->ERNUM) return;

    MR_IN(8)

    convert(_MIPP_ n, mr_mip->w0);
    mr_select(_MIPP_ x, MINUS, mr_mip->w0, z);

    MR_OUT
}
